Thermosetting composition for exothermic hot tops



United States Patent 3,252,818 THEOSETTING COMPOSITION FOR EXOTHERMICHOT TOPS Ronald H. Cooper, Clare, and Robert D. Goodenough and Gerald M.Corbett, Midland, Mich, assignors to The Dow Chemical Company, Midland,Mich., a corporation of Delaware Filed May 1, 1963, Ser. No. 277,231 2Claims. (Cl. 106-217) This application is a continuation-in-part ofapplication Serial Number 99,171, filed March 29, 1961, now abandoned.

This invention relates to improved compositions for use in porousrefractory structures which will withstand heat at elevated temperaturessuch as are encountered upon contact with molten metals. Moreparticularly it is concerned with improved compositions utilizingmoldable exothermic compounds for the production of risers and hot topsused in the pouring of molten metals such as iron, ferrous alloys andsteels into certain mold forms and to a method of fabricating suchstructures.

Hot tops and risers, as is well known in the art, are devices that oftenare employed with molds during the pouring of iron and steel to keep themetal molten in the upper portion of the ingot for as long a period oftime as possible. These particularly are used in the pouring of killedsteels which undergo substantial contraction upon solidification fromthe molten state. In use, the hot top which is affixed to the top of themold acts as a feeder supply for the molten metal during itssolidification and accompanying contraction in a mold. The resultingshrinkage cavity, or pipe as it is commonly called, thus occurs in themetal held in the hot top or in the upper portion of the ingot andthereby increases the ingot yield. In recent years, the use ofexothermic hot topping compounds, as they have come to be known, hasreplaced for many operations the conventional insulating type refractorymaterials long used for these purposes.

It is a principal object of the present invention, therefore, to providecompositions for fabrication into exothermic hot tops, risers and thelike porous structures which are readily moldable, have a relativelyshort curing time, yield a non-hygroscopic end product and are quiteinexpensive.

It is also an object of the present invention to provide compositionsfor fabrication into exothermic hot tops and the like porous refractorystructures wherein polymerization of the binder is achieved by an acidicagent which does not decompose upon heating at the curing temperaturesnor liberates toxic materials at this temperature.

It is an additional object of the present invention to providecompositions which give ready ease of formation of strong and toughexothermic hot tops along with a minimum amount of after-cleaning of thefabricating apparatus.

It is a further object of the present invention to provide compositionsfor hot tops which, when used in metal pouring, maintain the metal inmolten conditions as long as possible and thereby minimize the severityof the piping in the metal formed in the mold.

It is an additional object of the present invention to providecompositions for use in the preparation of fabri- "ice compositionswhich readily are blended into homogeneous mixtures for the fabricationof exothermic hot tops and the like refractory structures.

These and other objects and advantages will become apparent from thedetailed description presented herein after and by reference to theaccompanying figure.

The drawing in the figure shows schematically a unitary exothermic hottop device prepared from a composition of the instant invention.

In accordance with the present invention, the compositions for use inporous exothermic refractory structures which will withstand heat atelevated temperatures comprise a commonly used exothermic fillermaterial such as a mixture of aluminum, oxidizing agents and refractorypowders and a binder system built around novel sugar polymers. In theproduction of hot tops, for example, the filler can comprise from aboutto about weight percent or more of the composition with the compositebinder system making up the balance.

Fillers useful in the present compositions are those particularmaterials conventionally used in the manufacture of exothermic hot topsand risers for ingot molds and castings. These materials include, forexample, mixtures of aluminum, oxidizing agents such as thermallyreducible metal oxides (manganese dioxide or iron oxide) and oxygencontaining salts and refractory powders. Additionally, metallic halidessuch as potassium chloride, sodium chloride and the like can beincorporated into the hot topping compound if desired. These lattermaterials, if added, impart a fluxing action on the aluminum particlesand promote good combustion of the exothermic mixture. The fillermaterial will be in particulated form as is commonly used in preparingthe exothermic fabrications. Another illustrative example of anexothermic hot topping composition known in the art is described in US.Patent No. 2,591,105. The material taught in this patent is acomposition formed from an oxidizable metal such as aluminum (30-50weight percent), metal oxide such as iron oxide or manganese oxide (5-20weight percent) i.e. in an amount substantially less than required tocompletely oxidize the aluminum and a fluoride suchas an alkali fluorideor alkali aluminum fluoride (1-5 weight percent) to facilitate the startof the reaction upon contact with molten metal and to facilitatemaintaining the reaction to completion. Additionally, this illustrativepatented composition can contain sodium nitrate (0-10 weight percent),bentonite (0-2 weight percent), core gum (2-7 weight percent) andgranulated grog (remainder).

The binder used in the improved compositions of the instant invention isa polymeric composition resulting from the acid polymerization ofmonosaccharide sugars, preferably by employing alkali metal hydrogensulfates as the acidic reaction promoter. These monosaccharides, such asglucose and fructose for example, can be blended directly with thefiller. However, conveniently the monosaccharides are produced in situby hydrolysis of readily obtainable inexpensive diand polysaccharidehexose sugars as are present in cane sugar, beet sugar, molasses andcorn sugar. The hydrolysis results in utilizing the same acidic materialas hydrolyzer which subsequently, at moderately elevated curingtemperatures, acts to give polymerization of the monosaccharides. In theproduction of the exothermic hot top and riser fabrications the amountof saccharide to be employed will range from about 3 percent to about 14percent by weight of theexothermic aggregate filler. Preferably thesugar concentration will range from about 6 to about 10 percent of theaggregate weight.

Use of a binder having a relatively high sugar content is not desirablefor those structures which will be subjected to relatively hightemperatures during metal pouring because of the problems that may beintroduced by undesirable decomposition of the binder.

For example, hot top devices which contain more than 14 percent byweight of polymerized sugars, may fire and smoke excessively, causeintolerable degrees of metal splattering and give carbonization of theingot. In fact, at such high sugar levels, the hot tops may not even becapable of the primary requisite to hold the hot metal during the.pouring of a heat. Also, at the higher sugar concentrations, the curedproduct displays a tendency to swell.

On the other hand, hot tops and the like structures prepared usingrelatively small amounts of sugars can result in refractory structureswhich do not have the requisite strength after curing.

Useful acidic materials for hydrolyzing and polymerizing the sugarsaccharides are acidic compounds (i.e., those having a hydrogenionization constant, Ka, greater than about 1x10 including both acidsand acidic salts that are non-volatile at the elevated curingtemperatures, which do not decompose within this range and which do notproduce undesirable decomposition of the polymerformin-g constituentsduring the curing stage. Further, the acidic materials will be solidswhich are molten at the curing temperatures. Particularly usefulmaterials are the alkali metal hydrogen sulfates, e.-g., sodiumbisulfate (NaHSO potassium bisulfate (KHSO and lithium bisulfate (LiHSOSodium bisulfate (NaHSO because of its ready availability, low cost andeffectiveness as a hydrolyzer and polymerizing agent has been found tobe particularly useful in the present polymer resin forming system.

Acid materials for use as hydrolyzers and polymerization promotersshould be stable at the curing temperatures employed. Thus, relativelylow boiling aqueous solutions of mineral acids such as hydrochloric,dilute nitric, dilute sulfuric, phosphoric, pyrophosphoric, acetic andthe like generally are not useful in the present compositions ashydrolyzers and polymerization promoters as they are volatile below thecuring temperatures employed. Therestore, they do not remain in contactwith the mix components for a sufficiently long period to give theneeded hydrolysis of polysaccharides and subsequent acid promotedpolymerization of the resulting monosaccharides into the thermosetbinder. Likewise, ammonium sulfate, ammonium persulfate, ammoniumsulfamate, ammonium acid sulfate, zinc chloride, monoammonium phosphateand the like are not suitable for use in the present process andcomposition as all of these produce the corresponding volatile acids atthe curing temperatures.

The amount of acid material to be used will vary depending upon thetotal amount and types of saccharide sugars present. Highly satisfactorypolymeric binders result wherein the amount of acidic material is fromabout 1 to about 8 percent of the particulate exothermic hot toppingcompound filler. Lower amounts of acid polymerization promoter areemployed advantageously when monosaccharides are used directly in thecomposition. Preferably, the amounts of acid will be somewhat less thanthe amount of sugar used; for example in an exothermic hot top utilizingfrom about 6 to about 10 percent sucrose correspondingly from about 1.5to about 4.5 weight percent of NaHSO is used as hydrolyzing andmonosaccharide polymerizing agent.

The actual binder formation is carried out in the presence of water as afiuidizing medium. 'From about 3 to about 8 weight percent of water(based on total composition weight) is added to the exothermicfiller-saccharideacid mixture. Preferably the amount of water will rangefrom about 5 to about 7 weight percent of the total binderfillercomposition. At higher concentrations, much above 9 weight percent, thestructures tend to sag while in the green condition. Also, dimensionalinstability of the resulting 'hot top results as the product may undergoundesirable swelling accompanied by the formation of surface cracksduring the curing operation. At water contents less than indicated, thecured product may be weak and friable.

The water can be satisfactorily added to a dry-blended mixture offillerand binder. Alternatively, an aqueous solution of the sugar-acidmaterial or a solution of the sugar is used instead of firstdry-blending the binder components with the aggregate and then temperingwith water.

However, very-satisfactory hot tops are produced by first dry blendingthe ingredients and in most applications and operations this techniquemay be preferred. In preparing the dry-blends, the saccharide and acidbinder components can be premixed and the blend then added to thefiller. Alternatively all of the dry components can be blendedsimultaneously.

The dry blend of binder-filler can be used directly as mixed, or, ifdesired, can be stored prior to use. The dry binder-alkali metalbisulfite mix also can be stored prior to its use in a refractorycomposition.

In either of the above suggested methods of dryblending, it is essentialto obtain a substantially uniform and thorough dispersion andinterblending of all the ingredients.

The curing of formed refractory structures prepared from the instantcompositions is achieved by heating the compositions at temperaturesfrom about 350 to about 450 F., and perferably at about 400 F. for aperiod of from about 5 to about 30 minutes. The time of cure variesdirectly, both on the temperature of cure and the thickness and/ or sizeof the device being cured. For conventional hot top fabrications thecure time ordinarily will range from about 8 to about 15 minutes.

Curing the fabrications prepared using the present compositions atthermosetting temperatures below that indicated can yield a relativelyweak structure as Well as cause difiiculties in the decomposition of thepolymeric binder upon contact with heat from the molten metal or othersources. Thus, such improperly cured hot top devices may evolveconsiderable quantities of fire and smoke upon contact with the moltenmetal and may severely carbonize the resultant solidified metal in amanner similar to that seen when excessive amounts of binder areemployed.

At curing temperatures higher than that given herein, degradation andsome premature burnout of the polymer with subsequent loss in bindingstrength may be encountered.

Additionally, if desired, small amounts, from about 0.5 to about 2weight percent refractory type minerals, iron oxides and other similarmaterials can be incorporated into the mix to give added thermal shockresistance to the cured product. Also, glues, molasses, pitch, cereals,bentonites, silica flour, sea coal and the like when added in similaramounts can act as thixotropic agents to give better green strength tothe formed, uncured device. Small amounts from about 0.25 to about 1.0percent by weight of thermosetting synthetic resins, e.g.,phenolformaldehyde resins, when incorporated into the blend can serve asstrength extenders.

To illustrate the utility of the present new and novel compositions, anexothermic hot top was prepared. In

preparing this device, a commercially available exothermic aggregate wascoated with about 8 percent (on the weight of the aggregate) of sucrose,about 3 weight percent NaHSO, and the mixture tempered with about Thewet, plastic green composition was dropped into a mold cavity of size asset forth above, rammed lightly and the top surface of the resultingformed product trowelled.

7 weight percent water. The coating was accomplished 5 The specimenswere cured at a predetermined temperaby adding the dry binder componentsto the filler and mixture for a given period of time after which thecompresing for about 5 minutes. The water then was added and sionstrength and surface hardness of the product samples the mixingcontinued for an additional 5 minutes. The were determined. resultingcomposition, as freshly prepared, was a damp, Table I, which follows,summarizes the results of a pliable and flowable mixture of bindercoated filler. number of tests run using various mix compositions andThis material was pressed by ramming into a unitary process variables.

TABLE I Binder Composition 1 (weight percent) Cure Minimum Test CureTime Temperature, Tensile Surface 4 Remarks N 0. (Min.) F. Strength,Hardness Sucrose NaHSO; H1O lbs/sq. in.

8.0 3.0 7. 0 10 400 170 90-93 Very good mix and core. 8.0 4.0 7.0 8 400150 95-97 Excellent mix and core. 8.0 2. 0 7. 0 14 400 140 90412 Goodmix and core. 6. 0 3. 0 7. 0 12 400 100 90-92 Fair mix and core. 8.0 3.08.0 10 450 130 90-95 Good mix and core. 8.0 3.0 7.0 10 400 150 85-87Goog mix, not as tacky 8.0 2.0 6.0 12 400 135 85-87 G d mix and core.8.0 2.0 6. 0 14 350 140 85-87 Good mix and fair core. 8. 0 1.0 5.0 16350 130 85-88 Good mix and good core. 8.0 4. 0 7.0 12 350 120 85-87 Goodmix and fair core. 8. 0 3. 0 7. o 12 350 110 85-87 Do. 8. o a. 0 7. o 10400 100 75-80 10.0 3.0 7.0 12 400 125 90-92 Good mix. 10. 0 2. 3 s. 0400 120 85-87 Do.

39% sodium silicate (control sample) 80-85 1 Based on weight ofaggregate. 2 Commercial dried corn syrup was used in place of sucrose. 3Refined dextrose, or corn sugar, was used.

4 As determined using a Dietert A.F.S. approved hardness Tester.

hot top mold form under a pressure of about 80 pounds In a mannersimilar to that described for the foregoing per square inch. Theresulting satisfactory green hot example, exothermic risers, unitary hottops and sectional top was cured to hydrolyze and to polymerize thebinder hot tops and the like can be prepared using any of the componentsat a temperature of about 400 F. for about following as a binder system;glucose-potassium hydrogen 10 minutes. After this time, the thermosethot top in sulfate, ralfinose-sodium bisulfate, beet sugar-potassium theform of a strong rigid shape was removed from the bisulfate,maltose-lithium hydrogen sulfate, fructosecuring oven. potassiumhydrogen sulfate, sucrose-sodium hydrogen sul- The cured exothermic hottop was then employed in fate and the like. The binder-filler mixconcentrations conjunction with an ingot mold during the pouring of andtechniques to be used with these compositions are to hot top steelingots. The heat from the molten steel be those as set forthhereinbefore. being poured decomposed and burned out the cured It isunderstood that any of the useful saccharide sugars polymeric sugarbased resin and left a strong and unican be satisfactorily polymerizedby any of the listed formly porous refractory structure which providedan acidic materials. easy escape for the gases evolved from the moltenmetal. Various modifications can be made in the present in- Thestructure, after burnout of the binder, still was vention withoutdeparting from the spirit or scope thereof strong enough to withstandthe ferrostatic head developed for it is understood that we limitourselves only as defined by the charge of molten metal. in the appendedclaims.

After the ingot had been poured and solidified, the We claim: hot topwas readily broken away and stripped from the 1. In a thermosettingcomposition for the fabrication ingot. Substantially none of the burnedout. structure of exothermic hot tops characterized in beingthermosetadhere to the solidified metal. ting when heated to atemperature between about 350 In a similar manner, sectionalized hottops and risers d about 5 F- and consisting essentially of a particalsocan be fabricated, ulated exothermic hot topping compound aggregatefiller The following example will serve to further illustrate and abinder the improvement which comprises a binder the present inventionbut is not meant to limit it thereto. as based on the filler weight offrom about 6 to about 10 percent of a hexose saccharide selected fromthe group Example consisting of hexose monosaccharides and acidhydrolyzable polysaccharides and from about 1.5 to about 4.5 Test l 5 X5 2% Were P p 118mg a percent of an alkali metal acid sulfate selectedfrom the Commerclal xothefmlc hot PP g P group consisting of sodiumhydrogen sulfate, potassium The flggr'egate Was dry blwded Wlthsugijlf-sodlum acld hydrogen sulfate and lithium hydrogen sulfate, and,from S111fate @lflder Components al'ld the resultlng blend about 4 toabout 8 percent water, the water weight being PF Wlth Wale}? The coatingof f aggrflg'ate y based on the total weight of said filler-binder. b dr wa carr ed out by mechanically Il'llXlIlg the m- 2. In a thermosettingcomposition for the fabrication gredlents 111 a mlx'mullef for about 5 qof exothermic hot tops characterized in being thermoset- T Sodium acidSulfate WEIs ground, 8 a IIllCfO- ting when heated to a temperaturebetween about 350 pulverizer and passed through an 0.027 inch screen.The and about 450 F. and consisting essentially of a parsucrose was acommercial product and ground through ticulated exothermic hot toppingaggregate filler and a a micro-pulverizer mill before incorporation intothe binder, the improvement which comprises a binder based blend. on theweight of said aggregate of about 8 percent sucrose,

about 3 percent sodium hydrogen sulfate and about 7 percent by weightwater.

References Cited by the Examiner 2,996,759 8/1961 Smith 264-1093,021,566 2/1962 Sommer 264109 FOREIGN PATENTS UNITED STATES PATENTS 5785,984 11/1957 Great Britain.

9/1943 Happe 10640 10/1956 Gielow et 1 ALEXANDER H. BRODMERKEL, PrimaryExaminer.

7/1957 Pletsch et a1 22-147 3/1958 Jones ALFRED L. LEAVITT, Exammer 2/1959 Gogek 106 38,4 10 P- E- ANDERSON, D. ARNOLD, Assistant Examiners.

1. IN A THERMOSETTING COMPOSITION FOR THE FABRICATION OF EXOTHERMIC HOTTOPS CHARACTERIZED IN BEING THERMOSETTING WHEN HEATED TO A TEMPERATUREBETWEEN ABOUT 350 AND ABOUT 450*F. AND CONSISTING ESSENTIALLY OF APARTICULATED EXOTHERMIC HOT TOPPING COMPOUND AGGREGATE FILLER AND ABINDER THE IMPROVEMENT WHICH COMPRISES A BINDER AS BASED ON THE FILLERWEIGHT OF FROM ABOUT 6 TO ABOUT 10 PERCENT OF A HEXOSE SACCHARIDESELECTED FROM THE GROUP CONSISTING OF HEXOSE MONOSACCHARIDES AND ACIDHYDRO-